The present invention relates to a method for estimating and adjusting the short drop distance of a vehicle window glass in a frameless glass window system.
Frameless windows are common in convertible cars. Convertible cars have a canopy which can be moved from an extended position to a retracted position. In the retracted position of the canopy there is no part of the canopy which engages with the top edge of the window. However, in the extended position of the canopy the top edge of the window engages with at least a part of the canopy. In the extended position of the canopy, when the door is opened, the window glass has to be lowered to a position which is slightly below the fully closed position. When the door is shut, the window glass is raised to a fully closed position in which it seals into a seal extending along the canopy of the vehicle above the window. When a door handle is operated to open the door, the window glass is lowered out of the seal in the canopy to enable the door to be opened without interference between the seal and window glass during this process. This lowering of the window while opening the door is commonly referred to as “Short-Drop”. However, the distance for which the glass lowering is required to be such that the “daylight” maximum opening shall not exceed a predetermined limit. For example 4 mm according to US regulation FMVSS118 or maximum opening shall not exceed 12 mm according to Directive 2000/4/EC of the European Parliament. This is required because safety regulations require that if the glass is open for more than the predetermined limit, then during a window close operation, obstacle detection and reversal (commonly called as Anti-Pinch) should be active. However, the Anti Pinch detection cannot be activated unless the motor has attained a certain stable speed. Hence if the glass is lowered just slightly more than the predetermined limit, the chances are that safety regulations would not be met. On the other hand, if the glass is not sufficiently lowered, the seal will get damaged when the door is opened and closed or there will be damage to the glass itself.
Also, these specifications have to be met over the temperature range of −40 to +80 degrees centigrade. Lowering the window by big distances would be an irritant to the user and hence is not a good option.
The windows are usually operated through an electric motor which is associated with a mechanism for controlling the movement of the window glass. The electric motor is controlled by an Electronic Control Unit (ECU). The ECU usually has a hall sensor to determine the number of rotations of the motor which in turn represents the distance moved by the window glass. The motor is coupled to the glass through mechanical linkages including a cable. The position estimation in power windows is based on the motor rotations measured by the hall sensor. However, it does not accurately represent the glass position because the window glass does not start moving as soon as the motor moves because of the slack in the cable and the other mechanical linkages. When the window glass is lowered or raised for a small distance, the window glass does not move to an exact position due to the cable slack and other mechanical linkages. Hence there will be a position lag of the window glass and there is a need to calculate accurate position of the window glass and correct this position lag.